The Eastern arborvitae cultivar Smaragd is more often sold under the names Emerald or Emerald Green. Its flattened sprays of scaly, evergreen needles densely cover the upright, columnar silhouette, making it an exceptional shrub for creating garden hedges or screens. It also makes an attractive vertical accent in a mixed border. Best grown in full to partial sun, it survives a mix of sun and shade across the day. The more sunlight the better for it. Emerald arborvitae matures 12 to 15 feet tall and 3 to 5 feet wide. Grow it in U.S. Department of Agriculture Plant Hardiness Zones 2b through 7.
For the densest and fullest growth of branches and needles, plant it in full to partial sun where it receives at least six hours direct sun daily. Arborvitae grows in partial shade, but the habit becomes much looser and open. Siting it where a shifting mix of sun and shade occurs across the day keeps the Emerald arborvitae alive, but don't expect as fast or as full a shrub compared to one planted in more sunlight.
The quality and intensity of sunlight in the Southern United States, as well as the hotter summers, allow the Emerald arborvitae to grow and look healthy in a mix of sun and shade. In USDA zones 6 and 7 or at higher elevations, stronger sun rays in summer provide more light energy to the leaves even in dappled shade. Farther north, the sun's angle is lower, less intense, so dappled shade does not provide as much light for photosynthesis, and the shrub may look a bit thinner and loose. It hot summer regions, shade in the hottest part of the afternoon may be a benefit to diminish stress from dry soil.
Shade Tree Types
If deciduous trees cast shade onto the Emerald arborvitae from spring to fall, the shrub grows and looks better, since more sunlight reaches the arborvitae when the trees are barren from fall to spring. If the arborvitae is planted under evergreen trees, such as pines, shade occurs year-round. Expect the arborvitae to look scrawnier if planted under evergreen trees.
If planted in a mix of sun and shade, it's vital that the soil is fertile, moist but well-draining. A wet soil coupled with lower light hastens development of root rot and other fungal diseases. Good air circulation around Emerald arborvitae in shadier conditions also diminishes wet soil or foliage issues. If soils are moist to dry and irrigation is not readily available, the arborvitae may grow full of health once its roots are established. Keep the root ball evenly moist for the first six to 12 months after planting before letting only rainfall sustain the plant in the dappled shade location.